Tuesday, March 25, 2014

Food for thought: Omnivore’s dilemma

In case you pay attention to the latest paleontology news,
there’s been a lot of publicity towards the ever-growing case for giant
flightless birds being herbivores. Isotope analysis done on the Eocene
Gastornis and Pleistocene Genyornis suggest diets high in fruits (for
Gastornis) and grass (Genyornis), overturning the long-held assumption of them
as predators.http://link.springer.com/article/10.1007%2Fs00114-014-1158-2
So that’s that, it seems; we made a mistake, and now these brilliant scientists
have demoted these terrifying runners into placid, docile browsers according to
the headlines. http://link.springer.com/article/10.1007%2Fs00114-014-1158-2

Nope, at least, not as dramatically as people have done so
in the past.Humans often pride
themselves in uniqueness-we’re the only animal who has emotions, can
communicate in languages, and can eat anything we want. Now, all three are
false assumptions. Omnivores, if you
look at the world, make up more of the animals of the world than you would
expect.

For example, horses eat mostly grass, oats, fruits, and
other vegetation. Their teeth are superb for grinding the hard silicaceous
fiber into digestible mush. But horses do eat meat. Offer a horse a burger, and
they’ll take it. Their teeth and digestive system is not adapted for flesh, but
they can and will eat it if available. In the cold dry habitats of Central Asia and the poles, people have successfully fed
their horses raw or cooked meat, being able to sustain the animal when no
forage is available.There’s even a book
on the terrifying psychological aberration of horses consuming flesh, finding
it to their liking, and hunting and killing even humans for it. http://www.amazon.com/Deadly-Equines-Shocking-Meat-Eating-Murderous/dp/1590480031

Of course, these are only the most dramatic examples. Pigs
and primates are comfortable eating whatever they can chew. Both true pandas
and red pandas eat whatever they can find. You don’t even have to look that
far; the sharp incisors and strong teeth of rodents make them excellent
omnivores, and rats especially have used their omnivory to become one of the
most successful mammals ever.

Can we connect modern analogies to the prehistoric examples?
Sure. Let’s start with Deinocheirus. Deinocheirus is an ornithomimid, theropod
dinosaurs with small, beaked heads. They’re called ostrich dinosaurs for
obvious reasons-the head, neck, torso and legs are very similar, down to the
feathers.Ostriches and other ratites
like emus and rheas are omnivores; emus eat whatever plants are available,
along with whatever insects they can find. Ostriches are more herbivorous, but
again whatever they can fit in their mouth they can eat. The secret is their
gizzard- full of stomach stones or gastroliths that do all the chewing for
them. Gastroliths have also been found in ornithomimid skeletons, as well as
other dinosaurs. This not only allows them to eat fibrous plants, but small
bones and eggs. Rheas are more herbivorous but do eat meat, while cassowaries
eat much softer fruit and have been known to scavenge as well as eating other
plants and small animals. So, using ratites as a model, Deinocheirus could have
eaten anything it could fit in its mouth-even its own theropod relatives. http://www.avianweb.com/ratites.html

Daeodon’s only living relative is the hippopotamus, another
distant relative of pigs and whales. Hippos eat carrion from time to time as
well as the water plants they usually subsist on. One paper mentioned cannibalism
and predatory behavior on some occasions. http://www.newscientist.com/article/dn6818-cannibalism-may-have-spread-anthrax-in-hippos.html
Whales are entirely carnivorous, ranging from zooplankton and krill to other
whales, but they’re aquatic, so that’s not a fair comparison. Entelodonts have
often been compared to pigs, only huge and stupid, and pigs have proven
themselves excellent omnivores. Pigs and peccaries, either feral or wild, have
covered every continent but Antarctica.Entelodonts were much less successful to say
the least, but using hippos as an analogy we could assume these beasties using
their large sharp teeth to devour anything they could find.

Arctodus, the short faced bear, is closely related to the
spectacled bear of South America, a very
adaptable and mostly herbivorous species. Closer in dimensions and environment
is the brown bear or grizzly, and indeed their teeth are very similar to
primates and pigs as well as their diet. Isotope studies on Arctodus have
suggested an almost entirely carnivorous diet, while morphological tests have
argued for omnivory. Again, their craniodental similarity to brown bears argues
for an omnivorous diet.Brown bears,
like pigs, have been extremely successful, and have been found all over each of
the northern continents.Bears have been
observed eating any kind of animal or vegetable they could try, using their
powerful paws and strong jaws to acquire almost anything they want. Being
relatively slow hampers their ability to hunt down prey, so they eat mostly
vegetation, but they do kill and eat anything from rodents to bison if they can
catch it. The short-faced bear is different in proportions, but it’s very
likely it had a very similar lifestyle.

Oviraptorans are much less straightforward. Oviraptoran skulls
have large beaks and very developed upper and lower jaws. Oviraptor itself has
been found with a lizard in its stomach, while Citipati’s famous nest also
contained skulls of Byronosaurus (a Troodont) chicks, possible prey for either
mother or brood. Caudipteryx, on the
other hand, an earlier genus, has been found with gastroliths suggesting that
it could have easily eaten plants too. Early species have tiny teeth at the
front of the mouth (with the exception of the bucktoothed Incisivosaurus),
while the late Creteaceous forms like Oviraptor and Citipati lacked teeth
entirely. Their jaws could easily crush wood, bone, or shell, or cut through
fiber or flesh, using turtles and parrots as examples. https://www.duo.uio.no/bitstream/handle/10852/11785/Jansenx2008x-xBeakxmorphologyxinxoviraptoridsxxbasedxonxextantxbirdsxandxturtlesxxCompressedxpicturesx.pdf?sequence=1
Most parrots are herbivorous, but there are several omnivorous species, while
turtles vary in omnivory from the mostly herbivorous green sea turtle to the
more carnivorous leatherback. The same
is true for Ceratopsians; New Zealand’s kea, as their normal forage is quickly
exploited by sheep, have in turn turned to sheep as a food source, using their
sharp beaks to “graze” and “browse” on the sleeping sheep, sometimes killing
them. http://www.nature.com/nature/journal/v52/n1356/abs/052629b0.html

And that brings us back to Gastornis. There are many modern
herbivorous birds of similar proportions http://gwawinapterus.wordpress.com/2013/12/15/herbivorous-flightless-birds-and-their-big-heads/,
but that doesn’t make it a shut in case. First, there’s the question of
scale-none of the birds mentioned were six feet tall, and proponents of a
purely herbivorous Gastornis have never mentioned what local plant species
around could have provided the giant fruits and nuts that the overbuilt head
could have fed on.Sylvornis, the gigantic
megapode of New Caledonia
that was hunted to death by humans, is given as an example, but while insular
gigantism applies in this case, it does not in the case of Gastornis. You see,
the falling sea level converted the European islands of the Cretaceous into a
more recognizable form, while Gastornis’ presence in the uninterrupted forests
of Asia and North America are as far as
insular gigantism as you can get.Furthermore, like Gasotrnis, Sylvornis is extinct and its living
relatives are comparatively smaller heads and beaks. I’ll be more apt to take
the comparison seriously if I was shown the complete skull and skeleton of the
bird. The article also mentions Aepyornis and Pachyornis, but the resemblance
in skull shape and proportions is extremely fleeting.

Compare:

And it’s not as if large billed ground birds can’t be
carnivores, either. Ground hornbills have proportionally bigger heads than the
examples of herbivorous birds used, and they’re strictly carnivores.

So where does this leave us? Well, I’m not an ornithologist,
so I can’t think of a suitable analogy for Gastornis, nor am I a
palaeobotanist, so I can’t possibly name what plants existed in the early
Paleogene. I put the onus on those arguing for a herbivorous lifestyle on the
basis on beak morphology, and for those using isotopes, only one of many specimens
was analyzed and it was not compared to herbivorous birds, only the carnivorous
ones.

Yes, I concede that Gastornis did eat plant material,
although with that kind of head, it could have eaten whatever it wanted. Writers claiming Gastornis was “gentle”,
“harmless” are applying ridiculous stereotypes about herbivores, making leaps
in logic, and sensationalizing the discovery to get more readers. I don’t blame
scientists; I blame journalists, and that’s a rant for another day.

There is a spectrum here between the two extremes-

I’ll end this article with a quote by Sir Arthur Conan
Doyle’s character Professor George Edward Challenger-

"It
proves," he roared, with a sudden blast of fury, "that you are the
damnedest imposter in London--a
vile, crawling journalist, who has no more science than he has decency in his
composition!"

About Me

Hi everyone! You may know me already, but 99% of you won't. I've decided to make a blog for myself. I'm a anthropology student who has returned to his original passion for palaeontology. Ever since I was little, I've been fascinated with the weird and wonderful animals that have inhabited our planet and I've made this blog to keep this in my mind and hopefully in yours. Most people blog about their interests, and while I've got a range of interests-see history and anthropology above, not to mention zoology, astronomy, art, cooking, science fiction and fantasy films and literature, and a myriad of others, the one I want to do for a living is the study of Earth's ancient past.

On this blog I'll review papers, talk about fossils, museums, and taxa, review art, film, literature, and our culture's view of paleontology, and share memories and insights. I've been inspired by the far better blogs of professional palaeontologists, and I'll share them as time goes on. I'm also open to requests and questions of opinions, the latest palaeo news, and discussions with other fans informal and professional.

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